Voice-frequency calling system



April 16, 1929. H, 5, BLACK 1,709,554

VOICE FREQUENCY CALLING SYSTEM I Filed Jilly 20, 1927 /Z A5 v n l M5 1/7 T 5% i i g; w

A A A AvA I '35 3 23 I F/G Z b i Loc/u Cmcwn 70 Tau L/NE //vv/v TORHAROLD J. 5AA CK Patented Apr. 1 6.1929.

I UNITED STATES mnom) s. annex, or monrcram, NEW JERSEY, nssreivoa rBELL. TELEPHONE LABORATORIES, mconeonArEn, 01 NEW YORK, 1v. v nCORPORATION or NEW YORK.

VOICE-FREQUEN CY CALLING SYSTEM.

. Application. filed July 20.1927. Serial No. 207,067.

r This invention relates to circuits for differentiating between wavesof ditferent durations, and particularlyv to voice frequency calling orringing circuits for telephone systerns.

An object of theinvention is to diiferentiate between waves of differentdurations.

In systems, such as carrier telephone systems and those employing voicefrequency toll lines and using the lowerfr equency range for telegraphtransmission, it is often desirable to employ voice frequency waves forcalling or signaling; It is therefore necessary that thecalling-apparatus should differentiate between the calling waves andvoice waves of the same frequency. In a specific preferred embodimentofv this invention a relay is operated by voice .fre-.

quency waves in. a telephone line to open a direct connection betweenthe battery and the winding of a second relay. However, there isprovided in parallel with the direct connection a path comprising acondenser anda resistance in series so that the second relay ismaintained in its operated position-- by the current through thecondenser during the charging period, the length of WhlCh'lS determinedby the relative values of the capacity and resistance of the circuit.This period is made of such length. that if the operating waves arevoice waves the first relay will release before the condenser becomescharged and the direct connection to the winding of the second relaywill berestored, while if the operating waves ere callmgwaves, which aremaintained for a time relatively long compared to the time of a givenfrequency voice wave, the condenser will become charged and the secondrelay will release before the first is released. Thus the see-- I 0ndrelay will respond to the action of calling waves on the first relay,but not to the action of voice waves.

With the arrangement of this invention the condenser is caused todischarge through 9. gr

resistance of very low ,value so that even when the waves impressed onthe first relay are interrupted for a'very short interval the condenserwill completely discharge with the result that when the relay is againoperated the operator presses her ringing key, both a main and anauxiliary transmitting relay are provlded and a condenser is connectedin series with the winding of the auxiliary relay. The action of theoperator closes acir- I! PATENT: OFFICE.

cuit. of the main relay which impresses the calling wave on the line andcloses-the circuit of the auxiliary relay which makes a paralleloperating connectionto the circuit of the main relay. This arrangementassures that the main relay will beoperated for at least as long as thecharging period ofthe condenser. The invention is illustrated "in theccompanying drawing in which:

Fig. 1 shows diagrammatically one ein bodiment thereof in the receivingapparatus for a voice frequency calling circuit;

Fig. 2 shows diagrammatically an embodiment in a complete transmittingand receiving arrangement for a voicefrequency calling circuit; and

Fig. 3 shows -dia'graminatically tion of the circuit of Fig.2. h

Referring .to Fig. 1 there is shown a line 10 adapted to be connected toa signaling a modificasystem such as a telephone system over which aretransmitted calling currents ofv the same frequency range as. thesignalingor-voice cu rents. This line is connected to the windin of analternating current relay -11 through a filter comprising ananti-resonant circuit 12 in the series arm and a condenser 13 in theshunt arm. This'fiIter acts to at-- tenuate waves of frequencies otherthan those employed as calling currents. 7, When the relay is operated aconnection is made from relay 15,battery 16 to ground. .The relay 15 isprovided-with two armatures 17 and 18. The armature 18' is arranged oundthrough its armature. winding of.

in circuit with I the winding of a third relay 19 so that whenever therelay 15 operated for at least'a definite time interval relay 19 willrelease.

Ordinarily relay 19 is maintained operated through the circuit fromground through winding of relay 19, resistance 20, arm 21 and contact22of relay 15, battery 23 to ground.

When relay is operated the armature is brought up, breaking the contactbetween arm 21 and contact 22 and making a contact be tween the arm 21and the armature 18 so that I is controlled by the capacity ofthecondenser,

and the resistance of the circuit (primarily the resistance of theelement 20) When the relay 15 releases the condenser 24 dischargesthrough the resistance element 25 which may 7 be designed to have a verylow resistance as it need onlybe high enough to prevent the relaycontacts from burning while the condenser discharges. If the relay 15remains operated for a time longer thanthe charging period of thecondenser 24 the relay 19 will release making a connection from groundthrough'batter 26, armature 17, armature of relay 19 and winding ofrelay 27, causing the.

operation of the relay 27 and making a connection to the circuit 28 togive an indication that calling signals are being impressed on the line10.

Thus when waves of short duration such as voice waves are impressed onthe relay 11 "from line 10, the relay 15 will be operated,

but will release before the relay 19 releases. However, when callingcurrents which persist for a definite period of time longer than thecharging time of the condenser 24, are impressed upon the relay 11, therelay 15 will remain operated for a suflicient length of time to causethe release of the relay 19, thus ment 25 is made very low so that thecon' denser 24 will completely discharge even operating relay 27 andgiving an indication in'the circuit 28. The resistance of the elewhenthe operation of relay 15 is interrupted for a very short interval, thuspreventing the action of a rapid succession of waves of shortduration-"from building up the condenser charge to such a release.

Referring to Fig. 2, there is shown a line 30 connecting a local circuitto a toll line.

point that the relay 19 will Ordinarily low frequency ringing currentsimpressedupon the local circuit by the operatorkactuate the relay 31through thearmature of 'rela 32 and condenser 33. The operation of 'r'eay 31 makes. a connection from- 31 a holding connection from groundthrough battery 39, armature of relay 37, winding of relay 61 to ground,so that the relay 33 will be held in the operated position as long asthe relay 37 is operated, which in turn will re main operated for thecharging period of the condenser 35. Therefore, voice frequencycallingcurrent will be impressed on the toll line'for a period at leastas long as the charging period of the condenser 35. When the relays arereleased condenser 35 discharges through the resistance 40.

- he voice frequency calling current from the source 34 is of acomparatively low level and therefore will produce no undesirabledisturbance in the local circuit.-

Voice frequency. calling signals from the toll line e. g. of 500 cyclesare transmitted through the right-hand armatures of relay 61 (when inthe released position) and filter network 41 to the winding of relay 42,which is so arranged as tonormally complete a circuit from groundthrough armature of relay 42, winding of relay 43, battery 44 to ground.Relay 43 in turn is arran ed so that it is thus normally operated,making a connection from theground through its armature and right-handcontact, winding of relay 45, resistance 46, battery 47 to ground.However, when the relay 42 is operated by the voice frequencycallingcurrents relay 43 releases opening this circuit through the winding ofrelay 45. However, the circuit from the ground through battery 47,resistance 46, winding of relay 45,. condenser 48, i

and resistance 49 to ground is not broken, so

that the relay 45 will remain operated for the charging period of thecondenser 48 in a similar manner as in the clrcuit arrangement of Fig.1.However, if the currents whichoperate the relay 42 persist for alongertime than the charging period of the condenser 48, relay 45 willrelease, closing a connection from ground through armature and left handcontact of relay 43, armature of relay 45, winding of relay 32, battery50 to ground, causing the operation of relay 32 and making a connectionfrom the source of low fre quency ringing current 51 through theannatures of relay 32 to the local circuit.

r Fig. 3 shows a modification of the boxed in portion of the circuit ofFig. 2, the corresponding connections to the remainder of the relay 54is normally maintained operated similarly the receiving circuits may beactuby the connection from ground throu h the armature of relay 42,connection 52, wlnding of relay 54, battery 55 to ground. However, whentherelay 42 is operated this connection is brokenand the relay 54releases, closing a connection from battery 56 through re- .sistance 57,left-hand contact and armature of relay 54, winding of relay 58, andresistance 59. However, since the winding of relay 58 and ;resistance 59are shunted by condenser 60 relay 58 will not operate immediately. Thisparallel circuit has practically the same time constant as would acircuit of infinite inductance in that at first the current practicallyall passes through the condenser through the armature of relay 58,connection 53, winding of relay 32 and battery 50 to ground. Thisinterval is so determined, by proportioning the impedances of theelements of the circuit, that the relay 58 will not be operated byordinary signaling currents but only by the voice frequency callingcurrents which persist for a definite period.

The invention may advantageously be used on telephone toll lines orcarrier and radio systems, a feature being that ringing currents of lowstrength or amplitude may beused, comparable to'the strength of the telehone currents themselves. These low strengt currents are readilytransmitted by the vacuum tube repeaters of a toll line and by therepeaters and terminal circuits of a carrier or radio channel. It is tobe understood that the sending circuits illustrated in the drawings maybe connected either to voice frequency lines or to carrier or radiochannel apparatus for modulating carrier waves, and

ated directly by waves from a telephone transmission line or by wavesresulting from detection of modulated waves sent over a carrier or radiochannel. The claims are intended to apply both to transmission at thesignaling frequency level and to transmission by means of a carrier]wave as in carrier systems.

Whatis claimed is:

1. In combination, a. line adapted for, trans mitting waves of shortduration andwaves of rado orrelatively long duration both of the samefre-' quency range, a relay connected thereto and responsive towaves ofsaid frequency range,

a source of energy, a second relayconnected to said source andcontrolled by said first relay, and a condenser in circuit with saidsecond relay to prevent actuation of said secque-ncy range, a relayresponsive to waves of saidfrequency range, a second relay controlled bysaid first relay, and means for preventlng the actuation of said secondrelay except by waves which persist uninterrupted for at least adefinite period, said means comprising a condenser connected 1n circuitwith the winding of said second relay by the operation of said firstrelay and a path of low re-- sist'ance through which said condenserdischargesupon the interruption of the operation of said first relay.

3. In combination, a line adapted to transmit waves of short durationand waves of relatively long duration both of the same frequency range,a relay responsive to waves of said frequency range, a second relay tobe operated only by said waves of long duration, a source of current, anormally closed contact connecting said source to the winding of saidsecond relay and opened by the action of said first relay, connectionsincluding a series condenser for supplying current to the winding ofsaid second relay whereby on the opening of said contact said secondrelay will remain operated for the charging period of said condenser.

4. In combination, a telephone line, means for transmitting voicefrequency calling signals thereover, a relay responsive to said sig;nals, an armature and associated contact for said relay, a secondrelayhaving a winding, an armature and an associate contact, connectionsfor normally supplying operating current'to the winding of said secondrelay whereby after the response of said first re lay to waves in saidline, the second relay is held operated for the charging time of saidcondenser, to prevent said second relay from being responsive to wavesof short duration.

5. In combination, a line, a source of waves, a main relay forconnecting said source to the line, means for operating said relay, anauxiliary relay for maintaining the operation of said main relay, awinding for said auxiliary at least as long as the charging period ofthe condenser. a I

6. In combination, a line adapted for trans mitting'waves of shortduration andwaves of relatively long duration both of the same frequencyrange, a relay connected thereto and responsive to waves of saidfrequency range, a source of energy, a second relay com nected to saidsource, a condensergconnected in circuit with said second relay, andmeans relay dependent upon substantially complete charging of saidcondenser and prevent actuation of said second relay during thetransmission of said waves of short duration.

In witness WhereofI hereunto subscribe my name this 18th day of July, A.D., 1927.

HAROLD s. BLACK.

